Aristotle's voluminous writings on animals have often been marginalised in the history of philosophy. Providing the first full-length comprehensive account of Aristotle's biology, its background, content and influence, this Companion situates his study of living nature within his broader philosophy and theology and differentiates it from other medical and philosophical theories. An overview of empiricism in Aristotle's Historia Animalium is followed by an account of the general methodology recommended in the Parts of Animals. An account of the importance of Aristotle's teleological perspective and the fundamental metaphysics of biological entities provides a basis for understanding living capacities, such as nutrition, reproduction, perception and self-motion, in his philosophy. The importance of Aristotle's zoology to both his ethics and political philosophy is highlighted. The volume explores in detail the changing interpretations and influences of Aristotle's biological works from antiquity to modern philosophy of science. It is essential for both students and scholars.